Methods and materials for treating subterranean formations using a three-phase emulsion based fracturing fluid

ABSTRACT

An emulsion for hydraulic fracturing to provide a one-step delivery of a fracturing fluid and a breaker for hydraulic fracturing of a hydrocarbon-bearing formation is provided. The emulsion for hydraulic fracturing is a water-in-oil-in-water emulsion having an internal aqueous phase that includes a breaker, an external aqueous phase that includes a fracturing fluid and a proppant, and an intermediate hydrocarbon phase separating the internal aqueous phase and external aqueous phase. The emulsion may include nanometer-sized or micrometer-sized particles to form a Pickering emulsion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from U.S. Provisional Application No.62/505,456 filed May 12, 2017, and titled “METHODS AND MATERIALS FORTREATING SUBTERRANEAN FORMATIONS USING A THREE-PHASE EMULSION BASEDFRACTURING FLUID.” For purposes of United States patent practice, thisapplication incorporates the contents of the Provisional application byreference in its entirety.

BACKGROUND Field of the Disclosure

The present disclosure generally relates to hydraulic fracturing for oiland gas wells. More specifically, embodiments of the disclosure relateto the delivery of a fracturing fluid and a breaker to a formation.

Description of the Related Art

Hydraulic fracturing (also referred to as “fracking”) is used tostimulate production in hydrocarbon-containing formations by usingmaterials to break (“fracture”) a formation and release hydrocarbonssuch as oil and gas. After drilling a well, fracturing fluids such aswater or chemicals may be injected into the well to reach a sufficientpressure to induce fractures in the formation. A fracturing fluid maycontain proppants such as sand (referred to as “frac sand”) or ceramicbeads to hold open fractures created in the formation.

Fracturing fluid “cleanup” refers to the breaking down of components,such as a fracturing polymer, so that such components do not negativelyaffect production from a well. The chemical used to break down afracturing fluid is referred to as a “breaker.” However, use of breakerswith fracturing fluids may be challenging, as activation of the breakerand breaking of the fracturing fluid should optimally occur after thefluid has placed all the proppant inside fractures. Early activation ofthe breaker may result in premature breaking of the fracturing fluid andmay cause what is referred to as early proppant “screenout,” that is,when the proppant bridges across a perforation or flow area and suddenlyrestricts flow, resulting in a rapid rise in pump pressure. Moreover,temperature increases in a well may also increase the difficulty ofcontrolling the break time of a fracturing fluid.

SUMMARY

Embodiments of the disclosure include a three-phase emulsion for theone-step delivery of a fracturing fluid. The three-phase emulsionprovides improved control over the breaking of the fracturing fluid toprevent premature breaking of the fracturing fluid before placing theproppant inside induced fractures.

In one embodiment, an emulsion for hydraulic fracturing of a formationis provided. The emulsion includes a first aqueous phase having abreaker and an ester, a second aqueous phase having a fracturing fluidand a proppant, and a hydrocarbon phase separating the first aqueousphase and second aqueous phase. The emulsion is a solid-stabilizedemulsion stabilized by a plurality of polylactate particles. In someembodiments, the first aqueous phase and hydrocarbon phase arestabilized by a hydrophobic emulsifier. In some embodiments, thehydrophobic emulsifier includes sorbitan monooleate or polyethylenedipolyhydroxystearate. In some embodiments, the second aqueous phase andhydrocarbon phase are stabilized by a hydrophilic emulsifier. In someembodiments, the hydrophilic emulsifier includes a polysorbate, anonylphenol ethoxylate, a seed oil-based surfactant, or a specialtyalkoxylate. In some embodiments, the hydrocarbon phase is a fractionaldistillate of crude oil, a saturated hydrocarbon, an unsaturatedhydrocarbon, a branched hydrocarbon, a cyclic hydrocarbon, a fattyderivative of an acid, an ester, an ether, an alcohol, an amine, anamide, or an imide, and any combination thereof. In some embodiments,the water of the first aqueous phase includes a brine having at leastone inorganic salt. In some embodiments, the breaker of the firstaqueous phase includes sodium chlorite, sodium hypochlorite, sodiumbromate, sodium persulfate, ammonium persulfate, encapsulated sodiumpersulfate, potassium persulfate, ammonium persulfate, sodium peroxide,ammonium peroxide, or magnesium peroxide. In some embodiments, the waterof the second aqueous phase includes a brine having at least oneinorganic salt. In some embodiments, the fracturing fluid is guar,hydroxypropylguar, carboxymethylhydroxypropylguar, carboxymethylguar,carboxymethylcellulose, carboxymethylhydroxy-ethylcellulose, and anycombination thereof. In some embodiments, the emulsion has an oil-waterratio (OWR) in the range of 10:90 to 40:60. In some embodiments, theemulsion has a viscosity in the range of 15 centipoise (cP) to 50 cP at511 inverse seconds (s⁻¹) at 77° F. In some embodiments, the emulsionhas a viscosity of at least 19 cP for at least 6 hours at a temperatureof 200° F. In some embodiments, the emulsion is intact for at least 6hours at a temperature of 200° F. In some embodiments, each of theplurality of polylactate particles have a diameter in the range of 1micrometer (μm) to 100 micrometers.

In another embodiment, a method of forming a water-in-oil-in-wateremulsion for hydraulic fracturing of a formation is provided. The methodincludes combining a water-in-oil emulsion and an oil-in-water emulsionto form the water-in-oil-in-water emulsion. The water-in-oil emulsionincludes an internal phase having water, a breaker, and an ester, anexternal phase having a hydrocarbon, and a hydrophobic emulsifier. Theoil-in-water emulsion includes an internal phase having the water-in-oilemulsion, an external phase having water, a fracturing fluid, and aproppant, a hydrophobic emulsifier, and a plurality of polylactateparticles, such that the water-in-oil-in-water emulsion is asolid-stabilized emulsion. In some embodiments, the method includespreparing the water-in-oil emulsion. In some embodiments, the methodincludes preparing the oil-in-water emulsion. In some embodiments, thehydrophobic emulsifier includes sorbitan monooleate or polyethylenedipolyhydroxystearate. In some embodiments, the hydrophilic emulsifierincludes a polysorbate, a nonylphenol ethoxylate, a seed oil-basedsurfactant, or a specialty alkoxylate. In some embodiments, thehydrocarbon is a fractional distillate of crude oil, a saturatedhydrocarbon, an unsaturated hydrocarbon, a branched hydrocarbon, acyclic hydrocarbon, a fatty derivative of an acid, an ester, an ether,an alcohol, an amine, an amide, or an imide, and any combinationthereof. In some embodiments, the breaker of the first aqueous phaseincludes sodium chlorite, sodium hypochlorite, sodium bromate, sodiumpersulfate, ammonium persulfate, encapsulated sodium persulfate,potassium persulfate, ammonium persulfate, sodium peroxide, ammoniumperoxide, or magnesium peroxide. In some embodiments, the fracturingfluid is guar, hydroxypropylguar, carboxymethylhydroxypropylguar,carboxymethylguar, carboxymethylcellulose,carboxymethylhydroxy-ethylcellulose, and any combination thereof.

In another embodiment, hydraulic fracturing a formation is provided. Themethod includes introducing an emulsion to a target zone in a formation,the emulsion including a first aqueous phase having a breaker and anester, a second aqueous phase having a fracturing fluid and a proppant,and a hydrocarbon phase separating the first aqueous phase and secondaqueous phase. The emulsion is a solid-stabilized emulsion stabilized bya plurality of polylactate particles. In some embodiments, the targetzone of the formation has a temperature in the range of 150° F. to 300°F. In some embodiments, the emulsion is introduced as a fluid pill. Insome embodiments, the first aqueous phase and hydrocarbon phase arestabilized by a hydrophobic emulsifier. In some embodiments, thehydrophobic emulsifier includes sorbitan monooleate or polyethylenedipolyhydroxystearate. In some embodiments, the second aqueous phase andhydrocarbon phase are stabilized by a hydrophilic emulsifier. In someembodiments, the hydrophilic emulsifier includes a polysorbate, anonylphenol ethoxylate, a seed oil-based surfactant, or a specialtyalkoxylate. In some embodiments, the hydrocarbon phase is a fractionaldistillate of crude oil, a saturated hydrocarbon, an unsaturatedhydrocarbon, a branched hydrocarbon, a cyclic hydrocarbon, a fattyderivative of an acid, an ester, an ether, an alcohol, an amine, anamide, or an imide, and any combination thereof. In some embodiments,the breaker of the first aqueous phase includes sodium chlorite, sodiumhypochlorite, sodium bromate, sodium persulfate, ammonium persulfate,encapsulated sodium persulfate, potassium persulfate, ammoniumpersulfate, sodium peroxide, ammonium peroxide, or magnesium peroxide.In some embodiments, the fracturing fluid is guar, hydroxypropylguar,carboxymethylhydroxypropylguar, carboxymethylguar,carboxymethylcellulose, carboxymethylhydroxy-ethylcellulose, and anycombination thereof. In some embodiments, each of the plurality ofpolylactate particles have a diameter in the range of 1 micrometer (μm)to 100 micrometers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the components and formation of athree-phase emulsion in accordance with embodiments of the disclosure;and

FIG. 2 is a schematic diagram depicting a three-phase emulsion inaccordance with embodiments of the disclosure.

DETAILED DESCRIPTION

The present disclosure will be described more fully with reference tothe accompanying drawings, which illustrate embodiments of thedisclosure. This disclosure may, however, be embodied in many differentforms and should not be construed as limited to the illustratedembodiments. Rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey thescope of the disclosure to those skilled in the art.

As used in the disclosure, “in situ” refers to an event or occurrencewithin a hydrocarbon reservoir including but not limited tomethodologies, techniques and chemical reactions for enhancinghydrocarbon recovery from hydrocarbon reservoirs.

Embodiments of the disclosure include a three-phase emulsion to providea one-step delivery of a fracturing fluid and a breaker for hydraulicfracturing of a hydrocarbon-bearing formation. The three-phase emulsionfor hydraulic fracturing provides for the delivery of the fracturingfluid and the breaker without premature breaking of the fracturing fluidthat may result in early proppant screenout. As described in thedisclosure, the three-phase emulsion provides two control mechanisms todelay breaking of the fracturing fluid: 1) separation of the fracturingfluid and breaker in separate aqueous phases of the emulsion, and 2) insitu transition from a basic pH to an acidic pH to facilitate breakingof the emulsion over a time period.

The three-phase emulsion for hydraulic fracturing is awater-in-oil-in-water (w/o/w) emulsion having an internal aqueous phasethat includes a breaker, an external aqueous phase that includes afracturing fluid and a proppant, and an intermediate hydrocarbon phaseseparating the internal aqueous phase and external aqueous phase. Insome embodiments, the three-phase emulsion may be formed from a firstemulsion (referred to as a “primary” emulsion) having the internalaqueous phase and the intermediate hydrocarbon phase, and a secondemulsion (referred to as a “secondary” emulsion) having the externalaqueous phase and the first emulsion as the internal phase. Thus, asdescribed in the disclosure, the primary emulsion may include theinternal aqueous phase, the secondary emulsion may include the externalaqueous phase, and the hydrocarbon phase of the primary emulsion mayseparate the internal aqueous phase and the external aqueous phase. Thethree-phase emulsion may also include nanometer-sized (that is, sizes inthe range of about one nanometer (nm) to about 100 nm) ormicrometer-sized (that is, sizes in the range of about one micrometer(μm) to about 100 micrometers) particles to form a solid-stabilizedemulsion (also referred to as a “Pickering emulsion”).

The primary emulsion used to form the three-phase emulsion may be awater-in-oil (w/o) emulsion (also referred to as an “invert” emulsion)having an internal aqueous phase and a hydrocarbon as the external phase(also referred to as the “continuous” phase). The aqueous internal phaseof the primary emulsion may include water, a breaker, and an ester. Thewater of the aqueous internal phase may include fresh water or a brine.In some embodiments, the water of the aqueous internal phase may includea brine of inorganic salts. In some embodiments, the breaker may includeoxidizing agents, enzymes, acids, and any combination thereof. In someembodiments, the breaker may include sodium peroxide, ammonium peroxide,magnesium peroxide, and the like. In some embodiments, the breaker mayinclude sodium chlorite, sodium hypochlorite, sodium bromate, sodiumpersulfate, ammonium persulfate, encapsulated sodium persulfate,potassium persulfate, ammonium persulfate and the like. In someembodiments, the ester of the internal aqueous phase may includelactate, acetate, or other suitable esters.

As discussed infra, the hydrocarbon external phase of the primaryemulsion may include a fractional distillate of crude oil; a fattyderivative of an acid, an ester, an ether, an alcohol, an amine, anamide, or an imide; a saturated hydrocarbon; an unsaturated hydrocarbon;a branched hydrocarbon; a cyclic hydrocarbon; and any combinationthereof.

The primary emulsion may be formed using a hydrophobic emulsifier havinga hydrophile-lipophile balance (HLB) indicative of hydrophobicity (forexample, an HLB value less than about 6). In some embodiments, thehydrophobic emulsifier may be sorbitan monooleate (having an HLB valuein the range of about 4 to about 5) or polyethylenedipolyhydroxystearate (having an HLB value in the range of about 5 toabout 6). In other embodiments, the hydrophobic emulsifier may be a talloil fatty acid (having an HLB value in the range of about 3.5 to about4.5), such as, for example, oleic acid.

The secondary emulsion used to form the three-phase emulsion may be anoil-in-water (o/w) solid-stabilized emulsion having the primary emulsionas the internal phase and an aqueous external phase. The aqueousexternal phase may include water, a fracturing fluid, and a proppant.The water of the aqueous internal phase may include fresh water or abrine. In some embodiments, the water of the aqueous internal phase mayinclude a brine of inorganic salts.

The fracturing fluid used in the primary emulsion may include afracturing polymer. In some embodiments, the fracturing polymer may beguar, hydroxypropylguar, carboxymethylhydroxypropylguar, carboxymethylguar, carboxymethylcellulose, carboxymethylhydroxy-ethylcellulose, andany combination thereof. In some embodiments, the fracturing fluid mayinclude a gelling agent. Such gelling agents may include, for example,galactomannan gums, modified or derivative galactomannan gums, andcellulose derivatives. In other embodiments, the fracturing fluid mayinclude other suitable natural or synthetic polymers known in the art.

The secondary emulsion may be formed using a hydrophilic emulsifierhaving a HLB indicative of hydrophilicity (for example, an HLB value ofgreater than 8). In some embodiments, the hydrophilic emulsifier may bea polysorbate. In some embodiments, the hydrophilic emulsifier is Tween®manufactured by Croda International of Snaith, United Kingdom. In someembodiments, the hydrophilic emulsifier is Tween® 20 (having an HLBvalue in the range of about 16 to about 17) manufactured by CrodaInternational of Snaith, United Kingdom. In other embodiments, thehydrophilic emulsifier may be nonylphenol ethoxylate, a seed oil basedsurfactant, or a specialty alkoxylate, each of which may be obtainedfrom Dow Chemicals of Midland, Mich., USA.

In some embodiments, the secondary emulsion includes nanometer-sized ormicrometer-sized particles to form a solid-stabilized emulsion. In someembodiments, the nanometer or micrometer-sized particles are polylactateparticles. In some embodiments, the polylactate particles may bemicrometer-sized polylactide resin particles. In some embodiments, thepolylactide resin may be BioVert®, BioVert® H150, or BioVert® NWBmanufactured by Halliburton of Houston, Tex., USA.

In some embodiments, the three-phase emulsion may include a bufferingagent to maintain a pH of the three-phase emulsion. In some embodiments,the buffering agent may be BA-20™ buffering agent manufactured byHalliburton Company of Houston, Tex., USA. In some embodiments, the pHof the three-phase emulsion may be about 6.5.

The three-phase emulsion may be formed from the primary emulsion and thesecondary emulsion, such that the secondary emulsion has an internalphase that includes the primary emulsion and the external aqueous phasedescribed supra. After formation of the three-phase emulsion from theprimary emulsion and secondary emulsion, the aqueous internal phase ofthe primary emulsion and the aqueous external phase of the secondaryemulsion are separated by a hydrocarbon phase (that is, the hydrocarbonexternal phase of the primary emulsion). As mentioned supra, thehydrocarbon phase of the three-phase emulsion may include a fractionaldistillate of crude oil; a fatty derivative of an acid, an ester, anether, an alcohol, an amine, an amide, or an imide; a saturatedhydrocarbon; an unsaturated hydrocarbon; a branched hydrocarbon; acyclic hydrocarbon; and any combination thereof.

Embodiments of the three-phase emulsion may be used in an environmenthaving a basic pH in the range of about 8 to about 12 and a temperaturein the range of about 150° F. to about 300° F. In such embodiments, theemulsion may break at an acidic pH of about 5 or less. Embodiments ofthe three-phase emulsion may have a viscosity in the range of about 15centipoise (cP) to about 50 cP at 511 inverse seconds (s⁻¹) at 77° F. Insome embodiments, the three-phase emulsion may have a flash point ofabout 200° C. or greater.

In some embodiments, the viscosity of the emulsion may be varied byvarying the oil-water ratio (OWR) of the emulsion. For example, theviscosity of the three-phase emulsion may be increased by increasing theOWR. In some embodiments, the OWR of the three-phase emulsion may be inthe range of about 10:90 to about 40:60. In some embodiments, thethree-phase emulsion may have an OWR of 10:90.

FIG. 1 is a schematic diagram 100 illustrating the components andformation of the three-phase emulsion in accordance with embodiments ofthe disclosure. As shown in FIG. 1, an aqueous phase 102 of a breakerand an ester and a hydrophobic emulsifier in a hydrocarbon phase 104 areblended in a high shear blender (for example, a blender having a mixingspeed of at least 11,500 revolutions-per-minute (RPM)) to form awater-in-oil emulsion (that is, the primary emulsion 106) used to formthe three-phase emulsion. The primary emulsion 106 is shown as analternative depiction in block 110.

To prepare an oil-in-water emulsion having the primary emulsion as theinternal phase, a fracturing fluid, a proppant, an emulsifier, and solidstabilizing particles in an aqueous phase 112 and the primary emulsion106 are blended in a low shear blender (for example, a blender having amixing speed of less than 1000 RPM) to form a secondary emulsion 114 andproduce the three-phase emulsion 116. As shown in FIG. 1, the aqueousphase 112 and the primary emulsion 106 form the secondary emulsion 114having the primary emulsion 106 as the internal phase, such that thehydrocarbon phase 104 of the primary emulsion 106 separates the aqueousphases 102 and 112.

FIG. 2 is a schematic diagram of another depiction of the three-phaseemulsion 200 illustrating the solid-stabilized properties of thethree-phase emulsion in accordance with embodiments of the disclosure.As shown in FIG. 2, the 3-phase emulsion 200 may include an internalaqueous phase 204 that includes a breaker and an ester, a hydrocarbonphase 206, and an external aqueous phase 208 that includes thefracturing fluid and the proppant. As shown in FIG. 2, the internalaqueous phase 204 and the hydrocarbon phase 206 may be stabilized bynanometer-sized or micrometer-sized particles 210 (numbering of all theparticles 210 in FIG. 2 is omitted for clarity). As described supra, theparticles 210 may be nanometer-sized or micrometer-sized particles toenable formation of a solid-stabilized emulsion.

A process for hydraulic fracturing of a hydrocarbon-bearing formationmay include preparing the three-phase emulsion at the surface of awellsite in the manner described in the disclosure. The three-phaseemulsion may be delivered (for example, pumped downhole as a fluid pill)to a target zone in a hydrocarbon-bearing formation using techniquesknown in the art. As discussed supra, the three-phase emulsion mayenable delivery to the target zone to induce fractures in the targetzone without premature breaking of the fracturing fluid and ensureplacement of all or substantially all of the proppant inside the inducedfractures before activation of the breaker of the three-phase emulsion.In some embodiments, the delayed breaking of the fracturing fluidprovided by the three-phase emulsion may also enable longer pumpingtimes for delivery of the three-phase emulsion to the target zone.

In some embodiments, the delivery of the three-phase emulsion isperformed in a basic pH (for example, a pH in the range of about 8 toabout 12) environment to ensure stability of the three-phase emulsion.As the three-phase emulsion encounters elevated temperatures (forexample, temperatures in the range of about 150° F. to about 300° F.),the esters and polylactate may hydrolyze and produce a correspondingacid. As the pH decreases and becomes acidic, the emulsifiers of thethree-phase emulsion may deactivate, resulting in breakage of theemulsion. The fracturing fluid in the outer aqueous phase and thebreaker in the internal aqueous phase released from the broken emulsionmay react to break the fracturing fluid. Thus, the initial basic pHenvironment and transition to an acidic pH provides an additionalcontrol over the initiation of the reaction between the fracturing fluidand the breaker to further prevent premature breaking of the fracturingfluid and enable optimal placement of the proppant in the inducedfractures. In addition to the advantages described supra, use of thethree-phase emulsion for hydraulic fracturing leaves the target zonewater wet after breakage of the emulsion and fracturing fluid andeliminates the use of a post-fracturing acid flush due to the in situemulsion and fracturing fluid breakage. Additionally, thepost-fracturing clean-up of equipment used in the fracturing process maybe easier due to the aqueous base of the external phase of thethree-phase emulsion.

EXAMPLES

The following examples are included to demonstrate embodiments of thedisclosure. It should be appreciated by those of skill in the art thatthe techniques and compositions disclosed in the example which followsrepresents techniques and compositions discovered to function well inthe practice of the disclosure, and thus can be considered to constitutemodes for its practice. However, those of skill in the art should, inlight of the present disclosure, appreciate that many changes can bemade in the specific embodiments which are disclosed and still obtain alike or a similar result without departing from the spirit and scope ofthe disclosure.

The following non-limiting example of a three-phase emulsion wasprepared and evaluated against a linear gel sample without formation asa three-phase emulsion. The linear gel sample was prepared with a sodiumthiosulfate breaker and hydroxylpropyl guar (HPG) as a fracturing fluid.The pH of the sample was maintained using BA-20™ buffering agentmanufactured by Halliburton Company of Houston, Tex., USA. Thecomposition of the linear gel sample is shown in Table 1:

TABLE 1 Formulation of Linear Gel Sample Component Quantity Water, liter(L) 1 KCl, parts per thousand by mass (ppt) 20 HPG, ppt 20 Buffer,BA-20 ™, gallon per thousand (gpt) To 6.5 pH Gel Stabilizer, SodiumThiosulfate, ppt 10 Breaker, Sodium Persulfate, ppt 0.5

The preparation of the linear gel may be the same as the preparation of“Part B” described infra. The initial viscosity of the linear gel samplewas measured as 25 cP at 511 s⁻¹ at 77° F. After measuring the initialviscosity, the linear gel sample was heated in an oven at 200° F. in apressurized aging cell at a pressure of about 300 psi. The viscosity ofthe linear gel sample was measured after 2 hours and after 4 hours. Theviscosities (including the initial viscosities) were measured at 511 s⁻¹at 77° F. The measured viscosities of the linear gel sample are shown inTable 2:

TABLE 2 Viscosity of Linear Gel Sample Viscosity Measurement (cP)Initial Viscosity 25 Viscosity after 2 hours 17 Viscosity after 4 hours8

The example three-phase emulsion was prepared in accordance with thetechniques described supra. The primary emulsion (that is, thewater-in-oil emulsion) used to form the example three-phase emulsion wasprepared using a high speed mixer at a mixing speed of 11,500revolutions-per-minute (RPM). The aqueous phase of the primary emulsion(referred to as “Part A”) was formed from a KCl brine, N-Flow 408™filter cake breaker manufactured by Halliburton of Houston, Tex., USA,and a sodium persulfate breaker. The oil phase was formed from diesel.The emulsifier used in the primary emulsion was EZ MUL® NT emulsifiermanufactured by Halliburton of Houston, Tex., USA. The pH of the primaryemulsion was 11.

The composition of the primary emulsion used to form the examplethree-phase emulsion is shown in Table 3:

TABLE 3 Formulation of Example Primary Emulsion (Part A) ProductsQuantity BASE OIL, Diesel, barrels (bbl) 0.60 EZ MUL ® NT, parts perbillion by mass (ppb) 11 Lime, ppb 1.5 N-Flow 408 ™, milliliters (ml) 70KCl brine (20K ppm), ppb 0.30 Breaker, Sodium persulfate, ppt 0.5

The secondary emulsion (that is, the oil-in-water emulsion) used to formthe example three-phase emulsion was formulated using the linear geldescribed supra as the fracturing fluid component. The fracturing fluidlinear gel (referred to as “Part B”) was prepared by mixing water withKCl using at an overhead stirrer at 500 RPM. HPG was added at a rateslow enough to avoid fish eye formation. After addition of the HPG, themixture was then stirred for 5 minutes, and BA-20™ buffering agent andsodium thiosulfate gel stabilizer were added. The fracturing fluidlinear gel formulation was stirred for an additional 30 minutes toensure hydration of the HPG. The pH of the secondary emulsion aqueousphase (Part B) was 6.5.

The three-phase emulsion was then prepared by adding 25 ml of Tween® 20to 1 liter of Part A under continuous stirring by an overhead stirrer at500 RPM. After stirring for 2 minutes, 50 grams of BioVert® H150polylactide resin was added to the Part A-Tween® 20 mixture. Thismixture was then stirred for 5 minutes, after which the stirring speedwas increased to 1000 RPM. Next, 350 ml of Part B was added undercontinuous stirring. The final mixture was then stirred for 10 minutesto produce the example three-phase emulsion. The viscosity of theexample three-phase emulsion was measured as 25 cP at 511 s⁻¹ at 77° F.

The example three-phase emulsion was heated in an oven for 8 hours at200° F. in a pressurized aging cell. The viscosity of the examplethree-phase emulsion was measured at 2 hours, 4 hours, 6 hours, and 8hours. The viscosities were measured at 511 s⁻¹ at 77° F. The integrityof the example three-phase emulsion was also observed at the measurementperiods. The measured viscosities of the example three-phase emulsion,and the observed in are shown in Table 4:

TABLE 4 Viscosity of Example Three-phase Emulsion Viscosity EmulsionMeasurement (cP) Integrity Initial Viscosity 25 Intact Viscosity after 2hours 23 Intact Viscosity after 4 hours 22 Intact Viscosity after 6hours 19 Intact Viscosity after 8 hours 5 Broken

As indicated by the viscosity values and observations shown in Table 4,the three-phase emulsion remained intact for up to 6 hours without anysignificant reduction in viscosity. After 8 hours, the three-phaseemulsion destabilized and the linear gel was broken, as indicated by thedecreased viscosity of 5 cP. The pH of the broken emulsion was 3.5. Asshown by the results in Table 4, the example three-phase emulsionprovided control over breaking of the fracturing fluid at elevatedtemperatures for a period of up to 6 hours. In contrast, as shown by theviscosity values in Table 2, the linear gel without formulation in athree-phase emulsion began breaking at just 2 hours and was broken after4 hours.

Ranges may be expressed in the disclosure as from about one particularvalue, to about another particular value, or both. When such a range isexpressed, it is to be understood that another embodiment is from theone particular value, to the other particular value, or both, along withall combinations within said range.

Further modifications and alternative embodiments of various aspects ofthe disclosure will be apparent to those skilled in the art in view ofthis description. Accordingly, this description is to be construed asillustrative only and is for the purpose of teaching those skilled inthe art the general manner of carrying out the embodiments described inthe disclosure. It is to be understood that the forms shown anddescribed in the disclosure are to be taken as examples of embodiments.Elements and materials may be substituted for those illustrated anddescribed in the disclosure, parts and processes may be reversed oromitted, and certain features may be utilized independently, all aswould be apparent to one skilled in the art after having the benefit ofthis description. Changes may be made in the elements described in thedisclosure without departing from the spirit and scope of the disclosureas described in the following claims. Headings used described in thedisclosure are for organizational purposes only and are not meant to beused to limit the scope of the description.

What is claimed is:
 1. An emulsion for hydraulic fracturing of aformation, the emulsion comprising: a first aqueous phase comprising abreaker and an ester; a second aqueous phase comprising a fracturingfluid and a proppant; and a hydrocarbon phase separating the firstaqueous phase and second aqueous phase, wherein the emulsion is asolid-stabilized emulsion stabilized by a plurality of polylactateparticles, wherein the emulsion has a viscosity of at least 19centipoise (cP) and is intact for at least 6 hours at a temperature of200° F.
 2. The emulsion of claim 1, wherein the first aqueous phase andhydrocarbon phase are stabilized by a hydrophobic emulsifier.
 3. Theemulsion of claim 2, wherein the hydrophobic emulsifier comprisessorbitan monooleate, polyethylene dipolyhydroxystearate, or a tall oilfatty acid.
 4. The emulsion of claim 1, wherein the second aqueous phaseand hydrocarbon phase are stabilized by a hydrophilic emulsifier.
 5. Theemulsion of claim 4, wherein the hydrophilic emulsifier comprises apolysorbate, a nonylphenol ethoxylate, a seed oil-based surfactant, oran alkoxylate.
 6. The emulsion of claim 1, wherein the hydrocarbon phasecomprises a fractional distillate of crude oil, a saturated hydrocarbon,an unsaturated hydrocarbon, a branched hydrocarbon, a cyclichydrocarbon, a fatty derivative of an acid, an ester, an ether, analcohol, an amine, an amide, or an imide, and any combination thereof.7. The emulsion of claim 1, wherein the first aqueous phase comprises abrine comprising at least one inorganic salt.
 8. The emulsion of claim1, wherein the breaker of the first aqueous phase comprises sodiumchlorite, sodium hypochlorite, sodium bromate, sodium persulfate,ammonium persulfate, encapsulated sodium persulfate, potassiumpersulfate, ammonium persulfate, sodium peroxide, ammonium peroxide, ormagnesium peroxide.
 9. The emulsion of claim 1, wherein the secondaqueous phase comprises a brine comprising at least one inorganic salt.10. The emulsion of claim 1, wherein the fracturing fluid comprisesguar, hydroxypropylguar, carboxymethylhydroxypropylguar,carboxymethylguar, carboxymethylcellulose,carboxymethylhydroxy-ethylcellulose, and any combination thereof. 11.The emulsion of claim 1, wherein the emulsion has an oil-water ratio(OWR) in the range of 10:90 to 40:60.
 12. The emulsion of claim 1,wherein each of the plurality of polylactate particles have a diameterin the range of 1 micrometer (μm) to 100 micrometers.